Hematopoietic stem cells (HSCs) are of great interest for potential applications in regenerative medicine and gene therapy. Although transcriptional profiling has begun to elucidate genetic regulation of HSC quiescence and proliferation, emerging evidence suggests that epigenetic regulation may play an important role in development of the hematopoietic system. The lines of investigation proposed here will broaden our understanding of the epigenetic mechanisms controlling gene expression in HSCs as they undergo self- renewal and differentiation. The central portion of this proposal will use both cell culture and animal models to study these questions and I plan to use techniques from molecular biology, biochemistry, flow cytometry, fluorescence microscopy, and pharmacologic interference to investigate these hypotheses. When completed, this research will provide a better understanding of the regulation of gene expression in HSCs and differentiated hematopoietic cells and enable manipulation of these cells in vitro as a step toward expansion of HSC populations for clinical applications in gene therapy.